Dry insulated parts and method of manufacture

ABSTRACT

An engine component such as a cast iron engine exhaust manifold having an outer irregular-shaped surface is covered with an inorganic heat insulating layer preferably having a thermal conductivity in the range of from about 0.01 BTU/hr/ft/*F to 0.2 BTU/hr/ft/*F. An encapsulating, cast metal layer is formed over the insulating layer so that when hot fluids within the manifold reach temperatures of up to 2,000* F and higher, the temperature at the outer case metal layer does not exceed 450* F.

United States Patent [1 1 LaHaye [451 Feb. 11, 1975 DRY INSULATED PARTSAND METHOD OF MANUFACTURE [76] inventor: Paul G. LaHaye, 3 Adams St.,South Portland, Maine 04106 [22] Filed: May 24, 1973 [21] Appl. No.:363,725

Related U.S. Application Data [63] Continuation-impart of Ser. No264,199, June 19,

1972, abandoned.

[52] U.S. Cl 60/272, 60/321, 60/323,117/71M,117/138,138/149,161/139,164/98 [51] Int. Cl. F0lm 3/10 Field ofSearch 117/71 M, 71 R, 138, 94;

252/47 T; 106/15 FP, 272; 60/323, 320, 321, 60/282; 164/98, 35; 161/139;29/5275; 138/149, 142, 145; 23/111, 277

[56] References Cited UNITED STATES PATENTS 3,413,803 12/1968 Rosenlundet al. 60/282 3,424,226 1/1969 Steele 16.4/35 3,488,723 1/1970Veazie..... 60/323 3,568,723 3/1971 Sowards 60/272 3,581,494 6/1971Scheitline et a1. 60/323 3,610,317 10/1971 Benfield et al 164/353,709,772 l/1973 Rice 60/282 3,724,218 4/1973 Cole... 60/323 3,729,9375/1973 Hoolslad 60/272 OTHER PUBLlCATlONS United States Patent OfficeClassification Definitions for Class 117, pp. 117-122 c, October 1969.

Primary Examiner-Charles E. Van Horn Assistant Examiner-Michael W. BallAttorney, Agent, or FirmWolf, Greenfield & Sacks [57] ABSTRACT An enginecomponent such as a cast iron engine exhaust manifold having an outerirregular-shaped surface is covered with an inorganic heat insulatinglayer preferably having a thermal conductivity in the range of fromabout 0.01 BTU/hr/ft/F to 0.2 BTU/hr/ft/"F. An encapsulating, cast metallayer is formed over the insulating layer so that when hot fluids withinthe manifold reach temperatures of upto 2,000 F and higher, thetemperature at the outer case metal layer does not exceed 450 F.

7 Claims, 7 Drawing Figures SHEET 1 OF 2 t SUPERCHARGER MANIFOLD vENGINE DRY INSULATED PARTS AND METHOD OF MANUFACTURE RELATED APPLICATIONThis application is a continuation-in-part of applicants copendingpatent application Ser. No. 264,199 filed June 19, 1972 now abandoned.

BACKGROUND OF THE INVENTION Particularly in large engines such as marinediesel engines, the high temperature of the exhaust manifold, locatedbetween the engine exhaust gas passage and a supercharger as well as theexhaust piping from the engine supercharger to atmosphere and fornonsupercharged engines from the engine to the atmosphere, is known tocause problems. When flammable liquids or gases are present, hightemperatures at the external surface of the manifolds can cause a fireor explosion hazard. Moreover, such high temperatures can be asubstantial safety hazard since engine operators can be easily burned onaccidental contact with the manifolds.

The prior art has sought to alleviate this problem in most cases byproviding for various means for cooling the outside of the manifold.Such means often include the use of a fluid jacket to pass a coolingfluid around the manifold and thus reduce surface temperatures. However,the use of cooling fluids adds to the space and weight requirements ofpower packages due to the accessory pumps, radiators and fluid supplymeans which also add to cost. When manifolds and conduits are liquidcooled as between the engine exhaust gas passageway such as the cylinderhead and the supercharger, hot exhaust gases passed to the superchargerare reduced in temperature thus causing some drop in the energyavailable to the supercharger thus reducing the power available tosupply the engine with air for combustion resulting in lower enginepower output per unit of engine displacement. When engine exhaust gas ispassed through a reactor located in the engine exhaust manifold orpiping as part of an emission reduction system, the gas temperatureentering the reactor influences the performance of the reactor. Highertemperatures are desirable and the absence of a cooling medium in themanifold provides such higher temperatures. Engine power reduction canbe substantial, for example as much as 2% or more when temperatures inthe manifold are reduced to 850 F from a normal temperature of about l,lF. The power loss can be reduced by merely leaving the manifolduninsulated and uncooled but, here again, heat dissipation through theexposed iron or steel surfaces of the manifold causes a temperature lossand in addition, the safety problem is substantially multiplied.

It is not a problem to merely insulate the manifolds as by the use oforganic or inorganic insulating layers. However, such layers oftenbecome degraded by moisture or contaminated with hydrocarbons normallypresent around an operating engine unless they are protected. Suchhydrocarbon gases and liquids tend to degrade the insulation reducingitsresistance to the flow of heat and can cause fire hazards. Other meansof en-v capsulating such as fabricating covers by formed sheet metalhave proven costly and unsatisfactory in protecting the thermalinsulation from mechanical failures in handling of the sheet metal andmanifold casting in serill vice, and in preventing permeation anddegrading by hydrocarbons as well as other liquids and gases.

SUMMARY OF THE'INVENTION It is'an important object of this invention toprovide a dry, heat insulated engine part comprising a conduit for hotfluid flow, which engine part is efficiently heat insulated withminimized cost and complexity.

Another object of this invention is to provide an engine part having acomplex form in accordance with the preceding object which can bemanufactured without complicated procedures and in a highly efficientmanner with good reliability and with outstanding safety features.

Still another object of this invention is to provide a method of forminga dry, heat insulated engine part in accordance with the precedingobjects.

Additional objects of the invention are to provide external metalencapsulation totally enclosing the thermal insulation to preventdeterioration due to permeation of the thermal insulation by engine roomair borne contaminants and by contaminants accidently spilled on theinsulation.

According to the invention a dry, heat insulated metallic engine parthas a conduit therethrough allowing hot fluid flow as for example in anengine exhaust manifold. The part defines an outer irregularly-shapedsurface with an inorganic insulating layer overlying the surface andhaving a thermal conductivity preferably in the range of from about 0.01BTU/hr/ft/F to 0.2 BTU/hr/ft/F. A cast metallic, encapsulating layerconforms to the shape of the insulating layer and covers the insulatinglayer preferably encapsulating it. The engine part is designed to have asurface temperature at the surface of the encapsulating layer of belowabout 450 F at fluid temperatures within the conduit of from 500 F to atleast 2,000 F when the engine part is operated in normal atmospheric airenvironments with air temperatures from 60 to F.

In the preferred embodiment, the engine part is a cast iron or steelengine exhaust manifold or conduit having a conventionally irregularshape to suit the internal fluid flow and external geometric constraintsimposed by the over-all engine configuration. The insulation conforms tothe outer irregular configuration of the manifold as does an overlyingcast metallic encapsulating layer preferably having a thickness ofone-sixteenth to one-half inch which provides mechanical protection andpreferably hermetically encapsulates the insulation through sealing ofthe outer metallic layer to the engine part.

According to the method of this invention, an irregularly-shaped membersubject to operating temperatures in the range of from 500 F to at least2,000 F, is insulated by forming an inorganic self-supporting insulatinglayer over a surface of the member with the insulating layer defining anouter irregular configuration. A thin mechanically strong imperviousmetal casing is then formed over the insulating layer and sealed to themember to encapsulate the insulation by direct seals or through the useof heat flow restricting joining means. It is important that the methodof this invention provide a cast outer metallic layer over anirregularly shaped member which outer layer can be maintained at atemperature below 450 F regardless of the temperature of the underlyingengine part. In the preferred method, a transient coating such as wax isplaced over the insulation layer, a mold conforming to the so insulatedengine part is formed using the engine part as a form, the transientlayer is removed and the outer metallic layer cast directly in the moldreplacing the transient layer over the insulation layer and engine partpreferably at temperatures high enough to form required hermetic sealswith the engine part thus encapsulating the insulation.

In some cases the outer metallic layer can be cast first and sealed tothe metallic engine part with an insulation layer later formed to fillthe space between the metallic part and the cast layer.

It is a feature of this invention that engine efficiency can besubstantially increased by maintaining the heat within a manifold ratherthan dissipating any substantial portion of the heat to an outsideenvironment.

Another feature of the invention is its anti-pollution aspects when usedto maintain heat in a flowing gas which gas is later processed in areactor more efficiently since the heat is maintained to the reactorinlet.

Still another feature of the invention relates to the safety increasepermitted by encapsulation of the insulating layer, cooling of the outersurface and prevention of moisture or hydrocarbon contamination of aninsulating layer.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other features, objectsand advantages of the present invention will be better understood fromthe following specification when read in conjunction with theaccompanying drawings in which:

FIG. 1 is a top perspective view of an insulated exhaust manifold inaccordance with a preferred embodiment of this invention;

FIG. 2 is a bottom view thereof;

FIG. 3 is a cross sectional view thereof taken through line 3-3 of FIG.2;

FIG. 4 is a top perspective view of an element thereof;

FIG. 5 is a diagrammatic showing of the manifold connected between asupercharger and an engine;

FIG. 6 is a cross sectional view through line 66 of FIG. 2 showing amodified seal construction; and

FIG. 7 is a top view of the manifold before insulation is applied.

DESCRIPTION OF PREFERRED EMBODIMENTS With reference now to the drawingsand more particularly FIGS. 1 and 5, a preferred embodiment of an enginepart in the form of a heat insulated engine exhaust manifold 10 is shownfor mounting between an engine block 11 and an engine supercharger 12 asconventionally found in a marine diesel engine.

The manifold 10 comprises a conventional single or alloyed iron or steelfabricated or cast part 13 (FIG. 7) in a substantially conventional formhaving engine block rectangular mounting flanges 14, 15 and 16preferably provided with bolt holes 17 and bolt receiving notches 18 toallow the manifold to be attached to an engine block. The manifold 10receives hot fluid in the form of combustion gases passing through inletopenings 20, 21, and 22 converging to a center passageway extendingsubstantially from one closed end to the other closed end of themanifold and from thence through an outlet integral passageway openingat 23. Opening 23 carries an outwardly extending flange 24 with suitablebolt holes 24' for attachment to an engine supercharger. Hot gases fromthe engine cylinders pass in the direction of arrows 25 out of theopening 23 as known in the art.

The cast iron component 13 of the manifold 10 is of a conventionalirregular configuration. Overlying the outer configuration is aninsulating layer 31 formed of an inorganic material preferably having athermal conductivity in the range of from 0.01 BTU/hr/ft/F to 0.2BTU/hr/ft/F. The thickness of the insulation layer can be whatever isrequired to balance the heat from the cast iron component of themanifold portions which reaches substantially the temperature of the hotinside fluids or gases to an outside manifold temperature, at thesurface of a skin casing 40, to maintain the surface at a level below450 F and preferably lower for safety reasons. Insulation thicknesses offrom 0.] inch to L5 inches are preferred. Inorganic insulating materialssuch as Fiberfrax, a trademarked product of Carborundum Corporation ofNiagara Falls, N.Y., and comprising an aluminum silicate, Min-K, atrademarked product of Union Carbide Corporation of New York, N.Y., analuminum oxide powder, foamed ceramic, sand, refractory oxides, mixturesthereof and the like can be used for the insulating material. It isnecessary that the insulating material not be degraded at thetemperatures normally encountered in engine operation or encountered insubsequent casting processes of the outer metallic layer as will bedescribed.

The insulating layer is preferably formed with a substantially uniformthickness and preferably conforms to the outer configuration of the castiron component 13 of the manifold. However, in some cases, it may bedesirable to form the insulation layer with nonuniform thicknessesand/or with an outer configuration different than that of the outerconfiguration of the cast iron component. For example, thicker sectionsof insulation can be used at local points ofhigh heat flux as at theturn in the passageway illustrated in FIG. 3.

Preferably the insulating layer is directly adjacent the outer surfaceof the cast iron component 13 with no voids present. Over the insulatinglayer 31 is a thin metallic, outer skin casing layer 40 which is castand which acts to provide mechanical protection and encapsula tion tothe insulating layer. The cast layer 40 is preferably formed of a goodheat dissipating material such as aluminum, aluminum alloys which meltat low enough temperatures for casting and are non-destructive to theinsulating layer. It is preferred to use aluminum or magnesium or alloysthereof having a thermal conductivity of at least about 50 BTU/hr/ft/F.These materials serve to minimize local hot spots because of the highthermal conductivity of the layer 40. Materials such as carbon or alloysteel, cast iron and the like can also be used for the casing 40. Thincoatings are preferred, preferably in the range of from one-sixteenth toone-half inch. The layer 40 preferably has a substantially uniformthickness and entirely surrounds and conforms to the outer configurationof the insulating layer being bound thereto at least because of theencircling nature of the layer to the irregular configuration of themanifold.

In addition to the above considerations for selection of the metalmaterial of the outer skin layer 40, the material is preferably designedto have a suitable coefficient of thermal expansion to the coefficientof thermal expansion of the component 13 over the expected operatingtemperature range of the component 13 and skin 40 so that the actualphysical differential in expansion between points on component 13 andbetween corresponding overlying points on skin 40 is as close to equalas possible at operating temperatures. Thus ideally for example, if themanifold is to be operated at a temperature of substantially l,00O F atthe component l3 and a resulting temperature of 400 F at the skin 40 thethermal expansion of part 13 at l,00O F is preferably equal to theexpansion of the skin 40 at 400 F. Although exact matching ofdifferential expansion at the two different operating temperatures isdifficult to obtain, careful selection of materials can result in onlysmall acceptable differences. For example, when the component 13 isformed of a ferritic material such as cast iron, ordinary carbon steelor a series 400 alloy steel having a thermal coefficient of expansion offrom 6 X 10' in/in/F to 8 X l0 in/in/F the skin material is preferablyselected to have a thermal coefficient of expansion of from 10 X 10'in/in/F to 12 X 10' inlin/"F and thus could be a cast aluminum or analuminum alloy. in this case, the physical expansion of the skin isclosely parallel to the physical expansion of the inner ferritic part.Assuming both the skin 40 and component 13 are both at 80 F and are thenheated to their operating temperatures as described above, thedifferent-ial expansion from point to point for the inner component 13and the outer skin 40 would be determined by:

ALI-2 1) r) 2) 2) 1 where AL, differential in thermal expansion L lineardistance between points over which thermal expansion takes place Ecoefficient of thermal expansion for material AT difference betweenstarting temperature and operating temperature subscript 1 refers to theinner component 13 and 2 refers to the encapsulating skin material. Inthe case described above with l,l00 F exhaust gas from an engine theinner part 13 metal temperature would be approximately l,00O F and thetypical length for an exhaust manifold would be 30 inches long, theinner part is iron and the outer encapsulating skin material is aluminumso that:

AL 30 [(1,000-80) (6 X 10") (400-80) (ll differential expansion AL 0.06in This difference in thermal expansion would be absorbed mechanicallyby the system. It is preferred that AL that is the differentialexpansion be maintained in the range of from 0 to 0.l0 inch. However,the value can vary depending on the specific sizes of parts used. If thedifferences in expansion characteristics are not matched, particularlywith long length or large diameter manifolds, they can cause destructionof the seals used or physical rupture of the skin or other parts of thedevice. In smaller manifolds, this feature is of lesser significancesince over-all physical expansion of parts is small.

Heat dissipating fins 30 are preferably integrally formed in the layer40. The fins improve natural convection to a surrounding fluidenvironment such as air, to dissipate the small amount of heat passingto the layer 40 through the insulation. The fins 30 have uni.- form finheights of three-fourth inch with widths of one-fourth inch and a fin tofin spacing of -1 inch although the dimensions can vary as desired andin some cases the fins can be eliminated.

In the case of an exhaust manifold, the jointbetween the outer metalliclayer 40 and the inner manifold 13 occurs at the flanges which connectthe manifold to the engine block and at the flange 24 which connects themanifold to the turbo supercharger. Since the engine block is liquidcooled, the manifold connecting flanges are only slightly hotter thanthe engine block to which they are connected. Thus, at this location,there is not sufficient heat flow from the manifold to the outermetallic layer to cause the external temperature to exceed the objectiveof keeping it below 450 F. At the other end, this is not the case. Thesupercharger is not liquid cooled and the connecting end of the manifoldpart 13 is at a high temperature. If it were directly connected to theouter metallic layer, a large heat leak would occur causing the outermetallic layer to exceed the desired temperature. In cases such as this,a flexible thin walled metallic seal is provided to restrict the flow ofheat from the manifold to the outer metallic layer.

The metallic layer 40 is preferably hermetically sealed to the cast ironor stainless steel component of the manifold during the castingoperation as by joints shown at 50 in FIG. 6 where the mounting flangesare overturned as shown, or by joints as shown in FIG. 3 directly topart 13 adjacent the flanges. Such joints are formed by contact of themolten outer layer with the part 13 during the casting process as willbe described. Such joints are preferably made at the lower temperatureor inlet end of the manifold where there is no great heat dissipation inoperation, from the cast iron section of the manifold to the outer skindue to the small area of contact and the cooler operating temperature ofthis end of the manifold. At the outlet end 23 of the manifold, wheretemperature of the manifold is highly elevated, it is preferred to sealthe outer metallic layer 40 to the inner cast iron or stainless steelcomponent 13 through a heat restricting seal ring such as 51. The sealring 51 is a convoluted circumferentially extending enclosing collarwith its inner cylindrical surface 52 bonded to the cast iron component13 of the manifold as by weldingor brazing and its outer cylindricalsurface 53-sealed directly to the skin or outer metallic layer 40 duringcasting procedure. The ring 51 is preferably formed of a low thermalconductivity metal in a thin convoluted encircling shape. For example,the ring can be formed of titanium or sheet steel having a thickness offrom 0.01 to 0.03 inch to restrict heat flow. The ring is preferablyresilient and can flex to allow for a small differential in expansionbetween the encapsulating layer 40 and the component 13 withoutdestruction of the seal.

Because of the metallic mechanical properties of the outer skin 40, itprovides mechanical protection to the insulating layer. In addition, itcan be sealed as described above to prevent moisture, hydrocarbons orother fluids from contaminating the insulating layer as could otherwisebe the case during normal operation of the engine. By proper selectionof materials and design of layer thicknesses, it is possible to obtainany reasonable desired temperature at the outer layer 40. For example,when the gas flow in the manifold reaches temperatures of 900 F, by theuse of the construction noted, the outer skin temperature can easily bemaintained below 350 F.

In the preferred method of this invention, the manifold cast ironcomponent 13 is 24 inches from end to end having an outside diameter of5 inches with a ,7 roughly uniform wall thickness of one-fourth inch.Component 13 is coated with an inorganic insulating layer such asFiberfrax as by applying it in conventional castable form containing abinder. The cast insulation is coated with a ceramic paint or othersealer known in the art to seal the porous insulation preventingpermeation by the later applied molten metal.

The insulated part is then coated with a layer of a transient materialsuch as a hydrocarbon wax having a thickness of one-fourth inchcorresponding to the thickness desired for the outer metallic layer tobe cast thereover. Where fins are to be formed, they can be carved inthe wax. The so coated insulated part is then used as a form and aconventional sand casting mold is formed thereover conforming to theouter surface of the wax layer.

The temperature is raised to melt the wax and it runs out of the castingmold. Preferably the temperature of the part 13 and the mold is heatedapproximately to the melting temperature of aluminum and molten aluminumthen poured into the mold to form the cast layer 40 bonded to the ringcollar 51 and seals 50 during the casting operation. The mold is thencooled at ambient temperatures and the completed manifold removed.

The above preferred method is basically the lost wax" procedure forforming castings as well-known in the art. Application of this procedureto the specific materials and components noted has significantadvantages as pointed out above. Costs are lowered and mechanicallystrong, advantageous results are obtained. However, the cast coating 40can be formed by several other methods. For example, the insulation canbe formed around the part 13 and a metal outer coating provided bydipping in molten metal to build up the desired thickness of metallicouter layer 40. In still another procedure, a wooden patternrepresenting the external shape of the outer layer 40 is formed and asplit mold made of it. The part 13 is then coated with insulation andplaced in the mold so formed. The outer layer 40 is then cast around theinsulation. This method avoids the chance of contamination by wax. Inall of these methods, the use of the temperature of the molten metalliclayer aids in degassing the insulation and assuring removal ofcontaminants from the insulation.

In still another method, a pattern can be made for the exterior shape ofthe outer layer 40. A core is then made representing the shape of thepart 13 with its insulated coating. The aluminum or other metallic layer40 is then cast using the core in the mold formed from the pattern. Themold is preferably a two-piece mold allowing the layer 40 to be formedas a two-piece jacket which can be opened and resealed around the part13. The part 13 can then be left with an air gap in place of theinsulating layer or alternatively, filled with a powdered insulationafter sealing of the layer 40 to the part 13. Preferably the space isevacuated of moisture and other contaminants prior to filling through afill opening and then the opening is sealed to form the final product.

While a specific embodiment of this invention has been shown anddescribed, it should be understood that many variations are possible.For example, the engine part which is insulated by a dry insulatingmaterial need not be a manifold but could be other parts such ascylinder heads, liners, piping, casings and the like used in marineengines, diesel engines, gas turbine engines, steam generators and thelike wherever the presence of unburned hydrocarbons, moisture and thespillage of fuel and lubricating oil could tend to contaminate thermalinsulation not protected by a sealing capsule.

The seals formed are preferably formed as at the collar or ring 51 andseals 50. Such seals when formed during the casting operation uniteparts 13 and 40 forming tight seals which restrict the flow therethroughto a value small enough so that there is no problem with whatevernormally would pass through the seal. For example, if normal capillaryaction forces at one atmosphere pressure differential keep outcontaminants, moisture and fluids, such a seal is sufficient even thoughthe seal may not be a hermetic seal.

While the manifold part 13 is preferably cast iron or steel asconventionally used, other metallic parts can be insulated in accordancewith this invention. The configurations of these parts are normallyirregular in that geometrical, cylindrical, square or the like shapesare not present but irregular shapes are present in accordance withrequired engine specifications and the like. Thus, to form outer layers40 by machining, sheet metal forming and conventional fabricatingtechniques, would involve high expense. However, the casting procedureof this invention enables low cost formation of the required parts withthe required encapsulated insulation.

I claim:

1. A cast metallic engine part said part defining an outer irregularlyshaped surface and being formed of an iron-containing metal defining afluid carrying conduit therein uninterrupted by fluid seals,

an inorganic dry insulation layer overlying said outer surface andhaving a thermal conductivity in the range of from about 0.01BTU/hr/ft/F to 0.2 BTU/hr/ft/F, and a cast metallic, protectiveencapsulating layer conforming to the shape of and covering saidinsulating layer,

said cast encapsulating layer being formed of a metal having a highthermal conductivity and selected from the group consisting essentiallyof aluminum, magnesium and alloys of these metals, said encapsulatinglayer having a surface temperature below about 450 F at fluidtemperatures within said part of from 500 F to at least 2,000 F,

said cast metallic encapsulating layer having a thermal coefficient ofexpansion matched to the thermal coefficient of expansion of said partso that over-all expansion of said part and metallic encapsulating layerare closely parallel to each other over the operating temperature rangeof said part.

2. An engine part in accordance with claim 1 wherein said part is in theform of an engine exhaust manifold interconnected with an engine exhaustgas passage and a supercharger,

said manifold having an inlet and an outlet,

said cast metallic encapsulating layer being sealed to said conduit atsaid inlet and outlet.

3. An engine part in accordance with claim 1 wherein said insulatinglayer thickness is from about 0.1 to 1.5 inch and said metallicencapsulating layer has a thickness of from about one-sixth to one-halfinch.

4. An engine part in accordance with claim 1 wherein said cast metallicencapsulating layer has a thermal coefficient of expansion of from about10 X 10' to about 12 X 10" in/in/F and said part has a thermal coeffi-3,864,908 9 cient of expansion of from about 6 X 10 to about 8 groupconsisting essentially of aluminum and magne- X 10 in/in/F. Sium 5. Anengine part in accordance with claim 3 wherein An engine part inaccordance with claim 3 wherein said cast metallic la er carriesoutwardl extendin heat dissipating fins y y g 5 said one seal 18 formedby a convoluted metallic collar 6. An engine part in accordance withclaim 5 wherein Providing a long thin heat restricting P said cast layercomprises material selected from the UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent ,9 Dated February 11, 1975 Invenmfls)Paul G. LaI-Iaye It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 8, claim 3, last line of claim, change "one-sixth" to--one-sixteenth.

Signed and sealed this 29th day of April 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officerand Trademarks USCOMM- DC 60376-P69 Q 5. GOVERNMENT PRINTING OFFICE l90-856-8.

FORM PC4050 (10-69)

1. A CAST METALLIC ENGINE PART SAID PART DEFINING AN OUTER IRREGULARYSHAPED SURFACE AND BEING FORMED OF AN IRON-CONTAINING METAL DEFINING AFLUID CARRING CONDUIT THEREIN UNINTERRUPTED BY FLUID SEALS, AN INORGANICDRY INSULATION LAYER OVERLYING SAID OUTER SURFACE AND HAVING A THERMALCONDUCTIVITY IN THE RANGE OF FROM ABOUT 0.01 BTU/HR/FT/*F TO 0.2BTU/HR/FT/*F, AND A CAST METALLIC, PROTECTIVE ENCAPSULATING LAYERCONFORMING TO THE SHAPE OF AND COVERING SAID INSULATING LAYER, SAID CASTENCAPSULATING LAYER BEING FORMED OF A METAL HAVING A HIGH THERMALCONDUCTIVITY AND SELECTED FROM THE GROUP CONSISTING ESSENTIALLY OFALUMINUM, MAGNESIUM AND ALLOYS OF THESE METALS, SAID ENCAPSULATING LAYERHAVING A SURFACE TEMPERATURE BELOW ABOUT 450* F AT FLUID TEMPERATURESWITHIN SAID PART OF FROM 500* F TO AT LEAST 2,000* F, SAID CAST METALLICENCAPSULATING LAYER HAVING A THERMAL COEFFICIENT OF EXPANSION MATCHED TOTHE THERMAL COEFFICIENT OF EXPANSION OF SAID PART SO THAT OVER-ALLEXPANSION OF SAID PART AND METALLIC ENCAPSULATING LAYER ARE CLOSELYPARALLEL TO EACH OTHER OVER THE OPERATING TEMPERATURE RANGE OF SAIDPART.
 2. An engine part in accordance with claim 1 wherein said part isin the form of an engine exhaust manifold interconnected with an engineexhaust gas passage and a supercharger, said manifold having an inletand an outlet, said cast metallic encapsulating layer being sealed tosaid conduit at said inlet and outlet.
 3. An engine part in accordancewith claim 1 wherein said insulating layer thickness is from about 0.1to 1.5 inch and said metallic encapsulating layer has a thickness offrom about one-sixth to one-half inch.
 4. An engine part in accordancewith claim 1 wherein said cast metallic encapsulating layer has athermal coefficient of expansion of from about 10 X 10 6 to about 12 X10 6 in/in/*F and said part has a thermal coefficient of expansion offrom about 6 X 10 6 to about 8 X 10 6 in/in/*F.
 5. An engine part inaccordance with claim 3 wherein said cast metallic layer carriesoutwardly extending heat dissipating fins.
 6. An engine part inaccordance with claim 5 wherein said cast layer comprises materialselected from the group consisting essentially of aluminum andmagnesium.
 7. An engine part in accordance with claim 3 wherein said oneseal is formed by a convoluted metallic collar providing a long thinheat restricting path.